GNU Linux-libre 6.8.9-gnu

[releases.git] / net / sched / sch_qfq.c

// SPDX-License-Identifier: GPL-2.0-only
/*
 * net/sched/sch_qfq.c         Quick Fair Queueing Plus Scheduler.
 *
 * Copyright (c) 2009 Fabio Checconi, Luigi Rizzo, and Paolo Valente.
 * Copyright (c) 2012 Paolo Valente.
 */

#include <linux/module.h>
#include <linux/init.h>
#include <linux/bitops.h>
#include <linux/errno.h>
#include <linux/netdevice.h>
#include <linux/pkt_sched.h>
#include <net/sch_generic.h>
#include <net/pkt_sched.h>
#include <net/pkt_cls.h>


/*  Quick Fair Queueing Plus
    ========================

    Sources:

    [1] Paolo Valente,
    "Reducing the Execution Time of Fair-Queueing Schedulers."
    http://algo.ing.unimo.it/people/paolo/agg-sched/agg-sched.pdf

    Sources for QFQ:

    [2] Fabio Checconi, Luigi Rizzo, and Paolo Valente: "QFQ: Efficient
    Packet Scheduling with Tight Bandwidth Distribution Guarantees."

    See also:
    http://retis.sssup.it/~fabio/linux/qfq/
 */

/*

  QFQ+ divides classes into aggregates of at most MAX_AGG_CLASSES
  classes. Each aggregate is timestamped with a virtual start time S
  and a virtual finish time F, and scheduled according to its
  timestamps. S and F are computed as a function of a system virtual
  time function V. The classes within each aggregate are instead
  scheduled with DRR.

  To speed up operations, QFQ+ divides also aggregates into a limited
  number of groups. Which group a class belongs to depends on the
  ratio between the maximum packet length for the class and the weight
  of the class. Groups have their own S and F. In the end, QFQ+
  schedules groups, then aggregates within groups, then classes within
  aggregates. See [1] and [2] for a full description.

  Virtual time computations.

  S, F and V are all computed in fixed point arithmetic with
  FRAC_BITS decimal bits.

  QFQ_MAX_INDEX is the maximum index allowed for a group. We need
        one bit per index.
  QFQ_MAX_WSHIFT is the maximum power of two supported as a weight.

  The layout of the bits is as below:

                   [ MTU_SHIFT ][      FRAC_BITS    ]
                   [ MAX_INDEX    ][ MIN_SLOT_SHIFT ]
                                 ^.__grp->index = 0
                                 *.__grp->slot_shift

  where MIN_SLOT_SHIFT is derived by difference from the others.

  The max group index corresponds to Lmax/w_min, where
  Lmax=1<<MTU_SHIFT, w_min = 1 .
  From this, and knowing how many groups (MAX_INDEX) we want,
  we can derive the shift corresponding to each group.

  Because we often need to compute
        F = S + len/w_i  and V = V + len/wsum
  instead of storing w_i store the value
        inv_w = (1<<FRAC_BITS)/w_i
  so we can do F = S + len * inv_w * wsum.
  We use W_TOT in the formulas so we can easily move between
  static and adaptive weight sum.

  The per-scheduler-instance data contain all the data structures
  for the scheduler: bitmaps and bucket lists.

 */

/*
 * Maximum number of consecutive slots occupied by backlogged classes
 * inside a group.
 */
#define QFQ_MAX_SLOTS   32

/*
 * Shifts used for aggregate<->group mapping.  We allow class weights that are
 * in the range [1, 2^MAX_WSHIFT], and we try to map each aggregate i to the
 * group with the smallest index that can support the L_i / r_i configured
 * for the classes in the aggregate.
 *
 * grp->index is the index of the group; and grp->slot_shift
 * is the shift for the corresponding (scaled) sigma_i.
 */
#define QFQ_MAX_INDEX           24
#define QFQ_MAX_WSHIFT          10

#define QFQ_MAX_WEIGHT          (1<<QFQ_MAX_WSHIFT) /* see qfq_slot_insert */
#define QFQ_MAX_WSUM            (64*QFQ_MAX_WEIGHT)

#define FRAC_BITS               30      /* fixed point arithmetic */
#define ONE_FP                  (1UL << FRAC_BITS)

#define QFQ_MTU_SHIFT           16      /* to support TSO/GSO */
#define QFQ_MIN_LMAX            512     /* see qfq_slot_insert */
#define QFQ_MAX_LMAX            (1UL << QFQ_MTU_SHIFT)

#define QFQ_MAX_AGG_CLASSES     8 /* max num classes per aggregate allowed */

/*
 * Possible group states.  These values are used as indexes for the bitmaps
 * array of struct qfq_queue.
 */
enum qfq_state { ER, IR, EB, IB, QFQ_MAX_STATE };

struct qfq_group;

struct qfq_aggregate;

struct qfq_class {
        struct Qdisc_class_common common;

        struct gnet_stats_basic_sync bstats;
        struct gnet_stats_queue qstats;
        struct net_rate_estimator __rcu *rate_est;
        struct Qdisc *qdisc;
        struct list_head alist;         /* Link for active-classes list. */
        struct qfq_aggregate *agg;      /* Parent aggregate. */
        int deficit;                    /* DRR deficit counter. */
};

struct qfq_aggregate {
        struct hlist_node next; /* Link for the slot list. */
        u64 S, F;               /* flow timestamps (exact) */

        /* group we belong to. In principle we would need the index,
         * which is log_2(lmax/weight), but we never reference it
         * directly, only the group.
         */
        struct qfq_group *grp;

        /* these are copied from the flowset. */
        u32     class_weight; /* Weight of each class in this aggregate. */
        /* Max pkt size for the classes in this aggregate, DRR quantum. */
        int     lmax;

        u32     inv_w;      /* ONE_FP/(sum of weights of classes in aggr.). */
        u32     budgetmax;  /* Max budget for this aggregate. */
        u32     initial_budget, budget;     /* Initial and current budget. */

        int               num_classes;  /* Number of classes in this aggr. */
        struct list_head  active;       /* DRR queue of active classes. */

        struct hlist_node nonfull_next; /* See nonfull_aggs in qfq_sched. */
};

struct qfq_group {
        u64 S, F;                       /* group timestamps (approx). */
        unsigned int slot_shift;        /* Slot shift. */
        unsigned int index;             /* Group index. */
        unsigned int front;             /* Index of the front slot. */
        unsigned long full_slots;       /* non-empty slots */

        /* Array of RR lists of active aggregates. */
        struct hlist_head slots[QFQ_MAX_SLOTS];
};

struct qfq_sched {
        struct tcf_proto __rcu *filter_list;
        struct tcf_block        *block;
        struct Qdisc_class_hash clhash;

        u64                     oldV, V;        /* Precise virtual times. */
        struct qfq_aggregate    *in_serv_agg;   /* Aggregate being served. */
        u32                     wsum;           /* weight sum */
        u32                     iwsum;          /* inverse weight sum */

        unsigned long bitmaps[QFQ_MAX_STATE];       /* Group bitmaps. */
        struct qfq_group groups[QFQ_MAX_INDEX + 1]; /* The groups. */
        u32 min_slot_shift;     /* Index of the group-0 bit in the bitmaps. */

        u32 max_agg_classes;            /* Max number of classes per aggr. */
        struct hlist_head nonfull_aggs; /* Aggs with room for more classes. */
};

/*
 * Possible reasons why the timestamps of an aggregate are updated
 * enqueue: the aggregate switches from idle to active and must scheduled
 *          for service
 * requeue: the aggregate finishes its budget, so it stops being served and
 *          must be rescheduled for service
 */
enum update_reason {enqueue, requeue};

static struct qfq_class *qfq_find_class(struct Qdisc *sch, u32 classid)
{
        struct qfq_sched *q = qdisc_priv(sch);
        struct Qdisc_class_common *clc;

        clc = qdisc_class_find(&q->clhash, classid);
        if (clc == NULL)
                return NULL;
        return container_of(clc, struct qfq_class, common);
}

static const struct netlink_range_validation lmax_range = {
        .min = QFQ_MIN_LMAX,
        .max = QFQ_MAX_LMAX,
};

static const struct nla_policy qfq_policy[TCA_QFQ_MAX + 1] = {
        [TCA_QFQ_WEIGHT] = NLA_POLICY_RANGE(NLA_U32, 1, QFQ_MAX_WEIGHT),
        [TCA_QFQ_LMAX] = NLA_POLICY_FULL_RANGE(NLA_U32, &lmax_range),
};

/*
 * Calculate a flow index, given its weight and maximum packet length.
 * index = log_2(maxlen/weight) but we need to apply the scaling.
 * This is used only once at flow creation.
 */
static int qfq_calc_index(u32 inv_w, unsigned int maxlen, u32 min_slot_shift)
{
        u64 slot_size = (u64)maxlen * inv_w;
        unsigned long size_map;
        int index = 0;

        size_map = slot_size >> min_slot_shift;
        if (!size_map)
                goto out;

        index = __fls(size_map) + 1;    /* basically a log_2 */
        index -= !(slot_size - (1ULL << (index + min_slot_shift - 1)));

        if (index < 0)
                index = 0;
out:
        pr_debug("qfq calc_index: W = %lu, L = %u, I = %d\n",
                 (unsigned long) ONE_FP/inv_w, maxlen, index);

        return index;
}

static void qfq_deactivate_agg(struct qfq_sched *, struct qfq_aggregate *);
static void qfq_activate_agg(struct qfq_sched *, struct qfq_aggregate *,
                             enum update_reason);

static void qfq_init_agg(struct qfq_sched *q, struct qfq_aggregate *agg,
                         u32 lmax, u32 weight)
{
        INIT_LIST_HEAD(&agg->active);
        hlist_add_head(&agg->nonfull_next, &q->nonfull_aggs);

        agg->lmax = lmax;
        agg->class_weight = weight;
}

static struct qfq_aggregate *qfq_find_agg(struct qfq_sched *q,
                                          u32 lmax, u32 weight)
{
        struct qfq_aggregate *agg;

        hlist_for_each_entry(agg, &q->nonfull_aggs, nonfull_next)
                if (agg->lmax == lmax && agg->class_weight == weight)
                        return agg;

        return NULL;
}


/* Update aggregate as a function of the new number of classes. */
static void qfq_update_agg(struct qfq_sched *q, struct qfq_aggregate *agg,
                           int new_num_classes)
{
        u32 new_agg_weight;

        if (new_num_classes == q->max_agg_classes)
                hlist_del_init(&agg->nonfull_next);

        if (agg->num_classes > new_num_classes &&
            new_num_classes == q->max_agg_classes - 1) /* agg no more full */
                hlist_add_head(&agg->nonfull_next, &q->nonfull_aggs);

        /* The next assignment may let
         * agg->initial_budget > agg->budgetmax
         * hold, we will take it into account in charge_actual_service().
         */
        agg->budgetmax = new_num_classes * agg->lmax;
        new_agg_weight = agg->class_weight * new_num_classes;
        agg->inv_w = ONE_FP/new_agg_weight;

        if (agg->grp == NULL) {
                int i = qfq_calc_index(agg->inv_w, agg->budgetmax,
                                       q->min_slot_shift);
                agg->grp = &q->groups[i];
        }

        q->wsum +=
                (int) agg->class_weight * (new_num_classes - agg->num_classes);
        q->iwsum = ONE_FP / q->wsum;

        agg->num_classes = new_num_classes;
}

/* Add class to aggregate. */
static void qfq_add_to_agg(struct qfq_sched *q,
                           struct qfq_aggregate *agg,
                           struct qfq_class *cl)
{
        cl->agg = agg;

        qfq_update_agg(q, agg, agg->num_classes+1);
        if (cl->qdisc->q.qlen > 0) { /* adding an active class */
                list_add_tail(&cl->alist, &agg->active);
                if (list_first_entry(&agg->active, struct qfq_class, alist) ==
                    cl && q->in_serv_agg != agg) /* agg was inactive */
                        qfq_activate_agg(q, agg, enqueue); /* schedule agg */
        }
}

static struct qfq_aggregate *qfq_choose_next_agg(struct qfq_sched *);

static void qfq_destroy_agg(struct qfq_sched *q, struct qfq_aggregate *agg)
{
        hlist_del_init(&agg->nonfull_next);
        q->wsum -= agg->class_weight;
        if (q->wsum != 0)
                q->iwsum = ONE_FP / q->wsum;

        if (q->in_serv_agg == agg)
                q->in_serv_agg = qfq_choose_next_agg(q);
        kfree(agg);
}

/* Deschedule class from within its parent aggregate. */
static void qfq_deactivate_class(struct qfq_sched *q, struct qfq_class *cl)
{
        struct qfq_aggregate *agg = cl->agg;


        list_del(&cl->alist); /* remove from RR queue of the aggregate */
        if (list_empty(&agg->active)) /* agg is now inactive */
                qfq_deactivate_agg(q, agg);
}

/* Remove class from its parent aggregate. */
static void qfq_rm_from_agg(struct qfq_sched *q, struct qfq_class *cl)
{
        struct qfq_aggregate *agg = cl->agg;

        cl->agg = NULL;
        if (agg->num_classes == 1) { /* agg being emptied, destroy it */
                qfq_destroy_agg(q, agg);
                return;
        }
        qfq_update_agg(q, agg, agg->num_classes-1);
}

/* Deschedule class and remove it from its parent aggregate. */
static void qfq_deact_rm_from_agg(struct qfq_sched *q, struct qfq_class *cl)
{
        if (cl->qdisc->q.qlen > 0) /* class is active */
                qfq_deactivate_class(q, cl);

        qfq_rm_from_agg(q, cl);
}

/* Move class to a new aggregate, matching the new class weight and/or lmax */
static int qfq_change_agg(struct Qdisc *sch, struct qfq_class *cl, u32 weight,
                           u32 lmax)
{
        struct qfq_sched *q = qdisc_priv(sch);
        struct qfq_aggregate *new_agg;

        /* 'lmax' can range from [QFQ_MIN_LMAX, pktlen + stab overhead] */
        if (lmax > QFQ_MAX_LMAX)
                return -EINVAL;

        new_agg = qfq_find_agg(q, lmax, weight);
        if (new_agg == NULL) { /* create new aggregate */
                new_agg = kzalloc(sizeof(*new_agg), GFP_ATOMIC);
                if (new_agg == NULL)
                        return -ENOBUFS;
                qfq_init_agg(q, new_agg, lmax, weight);
        }
        qfq_deact_rm_from_agg(q, cl);
        qfq_add_to_agg(q, new_agg, cl);

        return 0;
}

static int qfq_change_class(struct Qdisc *sch, u32 classid, u32 parentid,
                            struct nlattr **tca, unsigned long *arg,
                            struct netlink_ext_ack *extack)
{
        struct qfq_sched *q = qdisc_priv(sch);
        struct qfq_class *cl = (struct qfq_class *)*arg;
        bool existing = false;
        struct nlattr *tb[TCA_QFQ_MAX + 1];
        struct qfq_aggregate *new_agg = NULL;
        u32 weight, lmax, inv_w;
        int err;
        int delta_w;

        if (NL_REQ_ATTR_CHECK(extack, NULL, tca, TCA_OPTIONS)) {
                NL_SET_ERR_MSG_MOD(extack, "missing options");
                return -EINVAL;
        }

        err = nla_parse_nested_deprecated(tb, TCA_QFQ_MAX, tca[TCA_OPTIONS],
                                          qfq_policy, extack);
        if (err < 0)
                return err;

        if (tb[TCA_QFQ_WEIGHT])
                weight = nla_get_u32(tb[TCA_QFQ_WEIGHT]);
        else
                weight = 1;

        if (tb[TCA_QFQ_LMAX]) {
                lmax = nla_get_u32(tb[TCA_QFQ_LMAX]);
        } else {
                /* MTU size is user controlled */
                lmax = psched_mtu(qdisc_dev(sch));
                if (lmax < QFQ_MIN_LMAX || lmax > QFQ_MAX_LMAX) {
                        NL_SET_ERR_MSG_MOD(extack,
                                           "MTU size out of bounds for qfq");
                        return -EINVAL;
                }
        }

        inv_w = ONE_FP / weight;
        weight = ONE_FP / inv_w;

        if (cl != NULL &&
            lmax == cl->agg->lmax &&
            weight == cl->agg->class_weight)
                return 0; /* nothing to change */

        delta_w = weight - (cl ? cl->agg->class_weight : 0);

        if (q->wsum + delta_w > QFQ_MAX_WSUM) {
                NL_SET_ERR_MSG_FMT_MOD(extack,
                                       "total weight out of range (%d + %u)\n",
                                       delta_w, q->wsum);
                return -EINVAL;
        }

        if (cl != NULL) { /* modify existing class */
                if (tca[TCA_RATE]) {
                        err = gen_replace_estimator(&cl->bstats, NULL,
                                                    &cl->rate_est,
                                                    NULL,
                                                    true,
                                                    tca[TCA_RATE]);
                        if (err)
                                return err;
                }
                existing = true;
                goto set_change_agg;
        }

        /* create and init new class */
        cl = kzalloc(sizeof(struct qfq_class), GFP_KERNEL);
        if (cl == NULL)
                return -ENOBUFS;

        gnet_stats_basic_sync_init(&cl->bstats);
        cl->common.classid = classid;
        cl->deficit = lmax;

        cl->qdisc = qdisc_create_dflt(sch->dev_queue, &pfifo_qdisc_ops,
                                      classid, NULL);
        if (cl->qdisc == NULL)
                cl->qdisc = &noop_qdisc;

        if (tca[TCA_RATE]) {
                err = gen_new_estimator(&cl->bstats, NULL,
                                        &cl->rate_est,
                                        NULL,
                                        true,
                                        tca[TCA_RATE]);
                if (err)
                        goto destroy_class;
        }

        if (cl->qdisc != &noop_qdisc)
                qdisc_hash_add(cl->qdisc, true);

set_change_agg:
        sch_tree_lock(sch);
        new_agg = qfq_find_agg(q, lmax, weight);
        if (new_agg == NULL) { /* create new aggregate */
                sch_tree_unlock(sch);
                new_agg = kzalloc(sizeof(*new_agg), GFP_KERNEL);
                if (new_agg == NULL) {
                        err = -ENOBUFS;
                        gen_kill_estimator(&cl->rate_est);
                        goto destroy_class;
                }
                sch_tree_lock(sch);
                qfq_init_agg(q, new_agg, lmax, weight);
        }
        if (existing)
                qfq_deact_rm_from_agg(q, cl);
        else
                qdisc_class_hash_insert(&q->clhash, &cl->common);
        qfq_add_to_agg(q, new_agg, cl);
        sch_tree_unlock(sch);
        qdisc_class_hash_grow(sch, &q->clhash);

        *arg = (unsigned long)cl;
        return 0;

destroy_class:
        qdisc_put(cl->qdisc);
        kfree(cl);
        return err;
}

static void qfq_destroy_class(struct Qdisc *sch, struct qfq_class *cl)
{
        struct qfq_sched *q = qdisc_priv(sch);

        qfq_rm_from_agg(q, cl);
        gen_kill_estimator(&cl->rate_est);
        qdisc_put(cl->qdisc);
        kfree(cl);
}

static int qfq_delete_class(struct Qdisc *sch, unsigned long arg,
                            struct netlink_ext_ack *extack)
{
        struct qfq_sched *q = qdisc_priv(sch);
        struct qfq_class *cl = (struct qfq_class *)arg;

        if (qdisc_class_in_use(&cl->common)) {
                NL_SET_ERR_MSG_MOD(extack, "QFQ class in use");
                return -EBUSY;
        }

        sch_tree_lock(sch);

        qdisc_purge_queue(cl->qdisc);
        qdisc_class_hash_remove(&q->clhash, &cl->common);

        sch_tree_unlock(sch);

        qfq_destroy_class(sch, cl);
        return 0;
}

static unsigned long qfq_search_class(struct Qdisc *sch, u32 classid)
{
        return (unsigned long)qfq_find_class(sch, classid);
}

static struct tcf_block *qfq_tcf_block(struct Qdisc *sch, unsigned long cl,
                                       struct netlink_ext_ack *extack)
{
        struct qfq_sched *q = qdisc_priv(sch);

        if (cl)
                return NULL;

        return q->block;
}

static unsigned long qfq_bind_tcf(struct Qdisc *sch, unsigned long parent,
                                  u32 classid)
{
        struct qfq_class *cl = qfq_find_class(sch, classid);

        if (cl)
                qdisc_class_get(&cl->common);

        return (unsigned long)cl;
}

static void qfq_unbind_tcf(struct Qdisc *sch, unsigned long arg)
{
        struct qfq_class *cl = (struct qfq_class *)arg;

        qdisc_class_put(&cl->common);
}

static int qfq_graft_class(struct Qdisc *sch, unsigned long arg,
                           struct Qdisc *new, struct Qdisc **old,
                           struct netlink_ext_ack *extack)
{
        struct qfq_class *cl = (struct qfq_class *)arg;

        if (new == NULL) {
                new = qdisc_create_dflt(sch->dev_queue, &pfifo_qdisc_ops,
                                        cl->common.classid, NULL);
                if (new == NULL)
                        new = &noop_qdisc;
        }

        *old = qdisc_replace(sch, new, &cl->qdisc);
        return 0;
}

static struct Qdisc *qfq_class_leaf(struct Qdisc *sch, unsigned long arg)
{
        struct qfq_class *cl = (struct qfq_class *)arg;

        return cl->qdisc;
}

static int qfq_dump_class(struct Qdisc *sch, unsigned long arg,
                          struct sk_buff *skb, struct tcmsg *tcm)
{
        struct qfq_class *cl = (struct qfq_class *)arg;
        struct nlattr *nest;

        tcm->tcm_parent = TC_H_ROOT;
        tcm->tcm_handle = cl->common.classid;
        tcm->tcm_info   = cl->qdisc->handle;

        nest = nla_nest_start_noflag(skb, TCA_OPTIONS);
        if (nest == NULL)
                goto nla_put_failure;
        if (nla_put_u32(skb, TCA_QFQ_WEIGHT, cl->agg->class_weight) ||
            nla_put_u32(skb, TCA_QFQ_LMAX, cl->agg->lmax))
                goto nla_put_failure;
        return nla_nest_end(skb, nest);

nla_put_failure:
        nla_nest_cancel(skb, nest);
        return -EMSGSIZE;
}

static int qfq_dump_class_stats(struct Qdisc *sch, unsigned long arg,
                                struct gnet_dump *d)
{
        struct qfq_class *cl = (struct qfq_class *)arg;
        struct tc_qfq_stats xstats;

        memset(&xstats, 0, sizeof(xstats));

        xstats.weight = cl->agg->class_weight;
        xstats.lmax = cl->agg->lmax;

        if (gnet_stats_copy_basic(d, NULL, &cl->bstats, true) < 0 ||
            gnet_stats_copy_rate_est(d, &cl->rate_est) < 0 ||
            qdisc_qstats_copy(d, cl->qdisc) < 0)
                return -1;

        return gnet_stats_copy_app(d, &xstats, sizeof(xstats));
}

static void qfq_walk(struct Qdisc *sch, struct qdisc_walker *arg)
{
        struct qfq_sched *q = qdisc_priv(sch);
        struct qfq_class *cl;
        unsigned int i;

        if (arg->stop)
                return;

        for (i = 0; i < q->clhash.hashsize; i++) {
                hlist_for_each_entry(cl, &q->clhash.hash[i], common.hnode) {
                        if (!tc_qdisc_stats_dump(sch, (unsigned long)cl, arg))
                                return;
                }
        }
}

static struct qfq_class *qfq_classify(struct sk_buff *skb, struct Qdisc *sch,
                                      int *qerr)
{
        struct qfq_sched *q = qdisc_priv(sch);
        struct qfq_class *cl;
        struct tcf_result res;
        struct tcf_proto *fl;
        int result;

        if (TC_H_MAJ(skb->priority ^ sch->handle) == 0) {
                pr_debug("qfq_classify: found %d\n", skb->priority);
                cl = qfq_find_class(sch, skb->priority);
                if (cl != NULL)
                        return cl;
        }

        *qerr = NET_XMIT_SUCCESS | __NET_XMIT_BYPASS;
        fl = rcu_dereference_bh(q->filter_list);
        result = tcf_classify(skb, NULL, fl, &res, false);
        if (result >= 0) {
#ifdef CONFIG_NET_CLS_ACT
                switch (result) {
                case TC_ACT_QUEUED:
                case TC_ACT_STOLEN:
                case TC_ACT_TRAP:
                        *qerr = NET_XMIT_SUCCESS | __NET_XMIT_STOLEN;
                        fallthrough;
                case TC_ACT_SHOT:
                        return NULL;
                }
#endif
                cl = (struct qfq_class *)res.class;
                if (cl == NULL)
                        cl = qfq_find_class(sch, res.classid);
                return cl;
        }

        return NULL;
}

/* Generic comparison function, handling wraparound. */
static inline int qfq_gt(u64 a, u64 b)
{
        return (s64)(a - b) > 0;
}

/* Round a precise timestamp to its slotted value. */
static inline u64 qfq_round_down(u64 ts, unsigned int shift)
{
        return ts & ~((1ULL << shift) - 1);
}

/* return the pointer to the group with lowest index in the bitmap */
static inline struct qfq_group *qfq_ffs(struct qfq_sched *q,
                                        unsigned long bitmap)
{
        int index = __ffs(bitmap);
        return &q->groups[index];
}
/* Calculate a mask to mimic what would be ffs_from(). */
static inline unsigned long mask_from(unsigned long bitmap, int from)
{
        return bitmap & ~((1UL << from) - 1);
}

/*
 * The state computation relies on ER=0, IR=1, EB=2, IB=3
 * First compute eligibility comparing grp->S, q->V,
 * then check if someone is blocking us and possibly add EB
 */
static int qfq_calc_state(struct qfq_sched *q, const struct qfq_group *grp)
{
        /* if S > V we are not eligible */
        unsigned int state = qfq_gt(grp->S, q->V);
        unsigned long mask = mask_from(q->bitmaps[ER], grp->index);
        struct qfq_group *next;

        if (mask) {
                next = qfq_ffs(q, mask);
                if (qfq_gt(grp->F, next->F))
                        state |= EB;
        }

        return state;
}


/*
 * In principle
 *      q->bitmaps[dst] |= q->bitmaps[src] & mask;
 *      q->bitmaps[src] &= ~mask;
 * but we should make sure that src != dst
 */
static inline void qfq_move_groups(struct qfq_sched *q, unsigned long mask,
                                   int src, int dst)
{
        q->bitmaps[dst] |= q->bitmaps[src] & mask;
        q->bitmaps[src] &= ~mask;
}

static void qfq_unblock_groups(struct qfq_sched *q, int index, u64 old_F)
{
        unsigned long mask = mask_from(q->bitmaps[ER], index + 1);
        struct qfq_group *next;

        if (mask) {
                next = qfq_ffs(q, mask);
                if (!qfq_gt(next->F, old_F))
                        return;
        }

        mask = (1UL << index) - 1;
        qfq_move_groups(q, mask, EB, ER);
        qfq_move_groups(q, mask, IB, IR);
}

/*
 * perhaps
 *
        old_V ^= q->V;
        old_V >>= q->min_slot_shift;
        if (old_V) {
                ...
        }
 *
 */
static void qfq_make_eligible(struct qfq_sched *q)
{
        unsigned long vslot = q->V >> q->min_slot_shift;
        unsigned long old_vslot = q->oldV >> q->min_slot_shift;

        if (vslot != old_vslot) {
                unsigned long mask;
                int last_flip_pos = fls(vslot ^ old_vslot);

                if (last_flip_pos > 31) /* higher than the number of groups */
                        mask = ~0UL;    /* make all groups eligible */
                else
                        mask = (1UL << last_flip_pos) - 1;

                qfq_move_groups(q, mask, IR, ER);
                qfq_move_groups(q, mask, IB, EB);
        }
}

/*
 * The index of the slot in which the input aggregate agg is to be
 * inserted must not be higher than QFQ_MAX_SLOTS-2. There is a '-2'
 * and not a '-1' because the start time of the group may be moved
 * backward by one slot after the aggregate has been inserted, and
 * this would cause non-empty slots to be right-shifted by one
 * position.
 *
 * QFQ+ fully satisfies this bound to the slot index if the parameters
 * of the classes are not changed dynamically, and if QFQ+ never
 * happens to postpone the service of agg unjustly, i.e., it never
 * happens that the aggregate becomes backlogged and eligible, or just
 * eligible, while an aggregate with a higher approximated finish time
 * is being served. In particular, in this case QFQ+ guarantees that
 * the timestamps of agg are low enough that the slot index is never
 * higher than 2. Unfortunately, QFQ+ cannot provide the same
 * guarantee if it happens to unjustly postpone the service of agg, or
 * if the parameters of some class are changed.
 *
 * As for the first event, i.e., an out-of-order service, the
 * upper bound to the slot index guaranteed by QFQ+ grows to
 * 2 +
 * QFQ_MAX_AGG_CLASSES * ((1<<QFQ_MTU_SHIFT)/QFQ_MIN_LMAX) *
 * (current_max_weight/current_wsum) <= 2 + 8 * 128 * 1.
 *
 * The following function deals with this problem by backward-shifting
 * the timestamps of agg, if needed, so as to guarantee that the slot
 * index is never higher than QFQ_MAX_SLOTS-2. This backward-shift may
 * cause the service of other aggregates to be postponed, yet the
 * worst-case guarantees of these aggregates are not violated.  In
 * fact, in case of no out-of-order service, the timestamps of agg
 * would have been even lower than they are after the backward shift,
 * because QFQ+ would have guaranteed a maximum value equal to 2 for
 * the slot index, and 2 < QFQ_MAX_SLOTS-2. Hence the aggregates whose
 * service is postponed because of the backward-shift would have
 * however waited for the service of agg before being served.
 *
 * The other event that may cause the slot index to be higher than 2
 * for agg is a recent change of the parameters of some class. If the
 * weight of a class is increased or the lmax (max_pkt_size) of the
 * class is decreased, then a new aggregate with smaller slot size
 * than the original parent aggregate of the class may happen to be
 * activated. The activation of this aggregate should be properly
 * delayed to when the service of the class has finished in the ideal
 * system tracked by QFQ+. If the activation of the aggregate is not
 * delayed to this reference time instant, then this aggregate may be
 * unjustly served before other aggregates waiting for service. This
 * may cause the above bound to the slot index to be violated for some
 * of these unlucky aggregates.
 *
 * Instead of delaying the activation of the new aggregate, which is
 * quite complex, the above-discussed capping of the slot index is
 * used to handle also the consequences of a change of the parameters
 * of a class.
 */
static void qfq_slot_insert(struct qfq_group *grp, struct qfq_aggregate *agg,
                            u64 roundedS)
{
        u64 slot = (roundedS - grp->S) >> grp->slot_shift;
        unsigned int i; /* slot index in the bucket list */

        if (unlikely(slot > QFQ_MAX_SLOTS - 2)) {
                u64 deltaS = roundedS - grp->S -
                        ((u64)(QFQ_MAX_SLOTS - 2)<<grp->slot_shift);
                agg->S -= deltaS;
                agg->F -= deltaS;
                slot = QFQ_MAX_SLOTS - 2;
        }

        i = (grp->front + slot) % QFQ_MAX_SLOTS;

        hlist_add_head(&agg->next, &grp->slots[i]);
        __set_bit(slot, &grp->full_slots);
}

/* Maybe introduce hlist_first_entry?? */
static struct qfq_aggregate *qfq_slot_head(struct qfq_group *grp)
{
        return hlist_entry(grp->slots[grp->front].first,
                           struct qfq_aggregate, next);
}

/*
 * remove the entry from the slot
 */
static void qfq_front_slot_remove(struct qfq_group *grp)
{
        struct qfq_aggregate *agg = qfq_slot_head(grp);

        BUG_ON(!agg);
        hlist_del(&agg->next);
        if (hlist_empty(&grp->slots[grp->front]))
                __clear_bit(0, &grp->full_slots);
}

/*
 * Returns the first aggregate in the first non-empty bucket of the
 * group. As a side effect, adjusts the bucket list so the first
 * non-empty bucket is at position 0 in full_slots.
 */
static struct qfq_aggregate *qfq_slot_scan(struct qfq_group *grp)
{
        unsigned int i;

        pr_debug("qfq slot_scan: grp %u full %#lx\n",
                 grp->index, grp->full_slots);

        if (grp->full_slots == 0)
                return NULL;

        i = __ffs(grp->full_slots);  /* zero based */
        if (i > 0) {
                grp->front = (grp->front + i) % QFQ_MAX_SLOTS;
                grp->full_slots >>= i;
        }

        return qfq_slot_head(grp);
}

/*
 * adjust the bucket list. When the start time of a group decreases,
 * we move the index down (modulo QFQ_MAX_SLOTS) so we don't need to
 * move the objects. The mask of occupied slots must be shifted
 * because we use ffs() to find the first non-empty slot.
 * This covers decreases in the group's start time, but what about
 * increases of the start time ?
 * Here too we should make sure that i is less than 32
 */
static void qfq_slot_rotate(struct qfq_group *grp, u64 roundedS)
{
        unsigned int i = (grp->S - roundedS) >> grp->slot_shift;

        grp->full_slots <<= i;
        grp->front = (grp->front - i) % QFQ_MAX_SLOTS;
}

static void qfq_update_eligible(struct qfq_sched *q)
{
        struct qfq_group *grp;
        unsigned long ineligible;

        ineligible = q->bitmaps[IR] | q->bitmaps[IB];
        if (ineligible) {
                if (!q->bitmaps[ER]) {
                        grp = qfq_ffs(q, ineligible);
                        if (qfq_gt(grp->S, q->V))
                                q->V = grp->S;
                }
                qfq_make_eligible(q);
        }
}

/* Dequeue head packet of the head class in the DRR queue of the aggregate. */
static struct sk_buff *agg_dequeue(struct qfq_aggregate *agg,
                                   struct qfq_class *cl, unsigned int len)
{
        struct sk_buff *skb = qdisc_dequeue_peeked(cl->qdisc);

        if (!skb)
                return NULL;

        cl->deficit -= (int) len;

        if (cl->qdisc->q.qlen == 0) /* no more packets, remove from list */
                list_del(&cl->alist);
        else if (cl->deficit < qdisc_pkt_len(cl->qdisc->ops->peek(cl->qdisc))) {
                cl->deficit += agg->lmax;
                list_move_tail(&cl->alist, &agg->active);
        }

        return skb;
}

static inline struct sk_buff *qfq_peek_skb(struct qfq_aggregate *agg,
                                           struct qfq_class **cl,
                                           unsigned int *len)
{
        struct sk_buff *skb;

        *cl = list_first_entry(&agg->active, struct qfq_class, alist);
        skb = (*cl)->qdisc->ops->peek((*cl)->qdisc);
        if (skb == NULL)
                qdisc_warn_nonwc("qfq_dequeue", (*cl)->qdisc);
        else
                *len = qdisc_pkt_len(skb);

        return skb;
}

/* Update F according to the actual service received by the aggregate. */
static inline void charge_actual_service(struct qfq_aggregate *agg)
{
        /* Compute the service received by the aggregate, taking into
         * account that, after decreasing the number of classes in
         * agg, it may happen that
         * agg->initial_budget - agg->budget > agg->bugdetmax
         */
        u32 service_received = min(agg->budgetmax,
                                   agg->initial_budget - agg->budget);

        agg->F = agg->S + (u64)service_received * agg->inv_w;
}

/* Assign a reasonable start time for a new aggregate in group i.
 * Admissible values for \hat(F) are multiples of \sigma_i
 * no greater than V+\sigma_i . Larger values mean that
 * we had a wraparound so we consider the timestamp to be stale.
 *
 * If F is not stale and F >= V then we set S = F.
 * Otherwise we should assign S = V, but this may violate
 * the ordering in EB (see [2]). So, if we have groups in ER,
 * set S to the F_j of the first group j which would be blocking us.
 * We are guaranteed not to move S backward because
 * otherwise our group i would still be blocked.
 */
static void qfq_update_start(struct qfq_sched *q, struct qfq_aggregate *agg)
{
        unsigned long mask;
        u64 limit, roundedF;
        int slot_shift = agg->grp->slot_shift;

        roundedF = qfq_round_down(agg->F, slot_shift);
        limit = qfq_round_down(q->V, slot_shift) + (1ULL << slot_shift);

        if (!qfq_gt(agg->F, q->V) || qfq_gt(roundedF, limit)) {
                /* timestamp was stale */
                mask = mask_from(q->bitmaps[ER], agg->grp->index);
                if (mask) {
                        struct qfq_group *next = qfq_ffs(q, mask);
                        if (qfq_gt(roundedF, next->F)) {
                                if (qfq_gt(limit, next->F))
                                        agg->S = next->F;
                                else /* preserve timestamp correctness */
                                        agg->S = limit;
                                return;
                        }
                }
                agg->S = q->V;
        } else  /* timestamp is not stale */
                agg->S = agg->F;
}

/* Update the timestamps of agg before scheduling/rescheduling it for
 * service.  In particular, assign to agg->F its maximum possible
 * value, i.e., the virtual finish time with which the aggregate
 * should be labeled if it used all its budget once in service.
 */
static inline void
qfq_update_agg_ts(struct qfq_sched *q,
                    struct qfq_aggregate *agg, enum update_reason reason)
{
        if (reason != requeue)
                qfq_update_start(q, agg);
        else /* just charge agg for the service received */
                agg->S = agg->F;

        agg->F = agg->S + (u64)agg->budgetmax * agg->inv_w;
}

static void qfq_schedule_agg(struct qfq_sched *q, struct qfq_aggregate *agg);

static struct sk_buff *qfq_dequeue(struct Qdisc *sch)
{
        struct qfq_sched *q = qdisc_priv(sch);
        struct qfq_aggregate *in_serv_agg = q->in_serv_agg;
        struct qfq_class *cl;
        struct sk_buff *skb = NULL;
        /* next-packet len, 0 means no more active classes in in-service agg */
        unsigned int len = 0;

        if (in_serv_agg == NULL)
                return NULL;

        if (!list_empty(&in_serv_agg->active))
                skb = qfq_peek_skb(in_serv_agg, &cl, &len);

        /*
         * If there are no active classes in the in-service aggregate,
         * or if the aggregate has not enough budget to serve its next
         * class, then choose the next aggregate to serve.
         */
        if (len == 0 || in_serv_agg->budget < len) {
                charge_actual_service(in_serv_agg);

                /* recharge the budget of the aggregate */
                in_serv_agg->initial_budget = in_serv_agg->budget =
                        in_serv_agg->budgetmax;

                if (!list_empty(&in_serv_agg->active)) {
                        /*
                         * Still active: reschedule for
                         * service. Possible optimization: if no other
                         * aggregate is active, then there is no point
                         * in rescheduling this aggregate, and we can
                         * just keep it as the in-service one. This
                         * should be however a corner case, and to
                         * handle it, we would need to maintain an
                         * extra num_active_aggs field.
                        */
                        qfq_update_agg_ts(q, in_serv_agg, requeue);
                        qfq_schedule_agg(q, in_serv_agg);
                } else if (sch->q.qlen == 0) { /* no aggregate to serve */
                        q->in_serv_agg = NULL;
                        return NULL;
                }

                /*
                 * If we get here, there are other aggregates queued:
                 * choose the new aggregate to serve.
                 */
                in_serv_agg = q->in_serv_agg = qfq_choose_next_agg(q);
                skb = qfq_peek_skb(in_serv_agg, &cl, &len);
        }
        if (!skb)
                return NULL;

        sch->q.qlen--;

        skb = agg_dequeue(in_serv_agg, cl, len);

        if (!skb) {
                sch->q.qlen++;
                return NULL;
        }

        qdisc_qstats_backlog_dec(sch, skb);
        qdisc_bstats_update(sch, skb);

        /* If lmax is lowered, through qfq_change_class, for a class
         * owning pending packets with larger size than the new value
         * of lmax, then the following condition may hold.
         */
        if (unlikely(in_serv_agg->budget < len))
                in_serv_agg->budget = 0;
        else
                in_serv_agg->budget -= len;

        q->V += (u64)len * q->iwsum;
        pr_debug("qfq dequeue: len %u F %lld now %lld\n",
                 len, (unsigned long long) in_serv_agg->F,
                 (unsigned long long) q->V);

        return skb;
}

static struct qfq_aggregate *qfq_choose_next_agg(struct qfq_sched *q)
{
        struct qfq_group *grp;
        struct qfq_aggregate *agg, *new_front_agg;
        u64 old_F;

        qfq_update_eligible(q);
        q->oldV = q->V;

        if (!q->bitmaps[ER])
                return NULL;

        grp = qfq_ffs(q, q->bitmaps[ER]);
        old_F = grp->F;

        agg = qfq_slot_head(grp);

        /* agg starts to be served, remove it from schedule */
        qfq_front_slot_remove(grp);

        new_front_agg = qfq_slot_scan(grp);

        if (new_front_agg == NULL) /* group is now inactive, remove from ER */
                __clear_bit(grp->index, &q->bitmaps[ER]);
        else {
                u64 roundedS = qfq_round_down(new_front_agg->S,
                                              grp->slot_shift);
                unsigned int s;

                if (grp->S == roundedS)
                        return agg;
                grp->S = roundedS;
                grp->F = roundedS + (2ULL << grp->slot_shift);
                __clear_bit(grp->index, &q->bitmaps[ER]);
                s = qfq_calc_state(q, grp);
                __set_bit(grp->index, &q->bitmaps[s]);
        }

        qfq_unblock_groups(q, grp->index, old_F);

        return agg;
}

static int qfq_enqueue(struct sk_buff *skb, struct Qdisc *sch,
                       struct sk_buff **to_free)
{
        unsigned int len = qdisc_pkt_len(skb), gso_segs;
        struct qfq_sched *q = qdisc_priv(sch);
        struct qfq_class *cl;
        struct qfq_aggregate *agg;
        int err = 0;
        bool first;

        cl = qfq_classify(skb, sch, &err);
        if (cl == NULL) {
                if (err & __NET_XMIT_BYPASS)
                        qdisc_qstats_drop(sch);
                __qdisc_drop(skb, to_free);
                return err;
        }
        pr_debug("qfq_enqueue: cl = %x\n", cl->common.classid);

        if (unlikely(cl->agg->lmax < len)) {
                pr_debug("qfq: increasing maxpkt from %u to %u for class %u",
                         cl->agg->lmax, len, cl->common.classid);
                err = qfq_change_agg(sch, cl, cl->agg->class_weight, len);
                if (err) {
                        cl->qstats.drops++;
                        return qdisc_drop(skb, sch, to_free);
                }
        }

        gso_segs = skb_is_gso(skb) ? skb_shinfo(skb)->gso_segs : 1;
        first = !cl->qdisc->q.qlen;
        err = qdisc_enqueue(skb, cl->qdisc, to_free);
        if (unlikely(err != NET_XMIT_SUCCESS)) {
                pr_debug("qfq_enqueue: enqueue failed %d\n", err);
                if (net_xmit_drop_count(err)) {
                        cl->qstats.drops++;
                        qdisc_qstats_drop(sch);
                }
                return err;
        }

        _bstats_update(&cl->bstats, len, gso_segs);
        sch->qstats.backlog += len;
        ++sch->q.qlen;

        agg = cl->agg;
        /* if the queue was not empty, then done here */
        if (!first) {
                if (unlikely(skb == cl->qdisc->ops->peek(cl->qdisc)) &&
                    list_first_entry(&agg->active, struct qfq_class, alist)
                    == cl && cl->deficit < len)
                        list_move_tail(&cl->alist, &agg->active);

                return err;
        }

        /* schedule class for service within the aggregate */
        cl->deficit = agg->lmax;
        list_add_tail(&cl->alist, &agg->active);

        if (list_first_entry(&agg->active, struct qfq_class, alist) != cl ||
            q->in_serv_agg == agg)
                return err; /* non-empty or in service, nothing else to do */

        qfq_activate_agg(q, agg, enqueue);

        return err;
}

/*
 * Schedule aggregate according to its timestamps.
 */
static void qfq_schedule_agg(struct qfq_sched *q, struct qfq_aggregate *agg)
{
        struct qfq_group *grp = agg->grp;
        u64 roundedS;
        int s;

        roundedS = qfq_round_down(agg->S, grp->slot_shift);

        /*
         * Insert agg in the correct bucket.
         * If agg->S >= grp->S we don't need to adjust the
         * bucket list and simply go to the insertion phase.
         * Otherwise grp->S is decreasing, we must make room
         * in the bucket list, and also recompute the group state.
         * Finally, if there were no flows in this group and nobody
         * was in ER make sure to adjust V.
         */
        if (grp->full_slots) {
                if (!qfq_gt(grp->S, agg->S))
                        goto skip_update;

                /* create a slot for this agg->S */
                qfq_slot_rotate(grp, roundedS);
                /* group was surely ineligible, remove */
                __clear_bit(grp->index, &q->bitmaps[IR]);
                __clear_bit(grp->index, &q->bitmaps[IB]);
        } else if (!q->bitmaps[ER] && qfq_gt(roundedS, q->V) &&
                   q->in_serv_agg == NULL)
                q->V = roundedS;

        grp->S = roundedS;
        grp->F = roundedS + (2ULL << grp->slot_shift);
        s = qfq_calc_state(q, grp);
        __set_bit(grp->index, &q->bitmaps[s]);

        pr_debug("qfq enqueue: new state %d %#lx S %lld F %lld V %lld\n",
                 s, q->bitmaps[s],
                 (unsigned long long) agg->S,
                 (unsigned long long) agg->F,
                 (unsigned long long) q->V);

skip_update:
        qfq_slot_insert(grp, agg, roundedS);
}


/* Update agg ts and schedule agg for service */
static void qfq_activate_agg(struct qfq_sched *q, struct qfq_aggregate *agg,
                             enum update_reason reason)
{
        agg->initial_budget = agg->budget = agg->budgetmax; /* recharge budg. */

        qfq_update_agg_ts(q, agg, reason);
        if (q->in_serv_agg == NULL) { /* no aggr. in service or scheduled */
                q->in_serv_agg = agg; /* start serving this aggregate */
                 /* update V: to be in service, agg must be eligible */
                q->oldV = q->V = agg->S;
        } else if (agg != q->in_serv_agg)
                qfq_schedule_agg(q, agg);
}

static void qfq_slot_remove(struct qfq_sched *q, struct qfq_group *grp,
                            struct qfq_aggregate *agg)
{
        unsigned int i, offset;
        u64 roundedS;

        roundedS = qfq_round_down(agg->S, grp->slot_shift);
        offset = (roundedS - grp->S) >> grp->slot_shift;

        i = (grp->front + offset) % QFQ_MAX_SLOTS;

        hlist_del(&agg->next);
        if (hlist_empty(&grp->slots[i]))
                __clear_bit(offset, &grp->full_slots);
}

/*
 * Called to forcibly deschedule an aggregate.  If the aggregate is
 * not in the front bucket, or if the latter has other aggregates in
 * the front bucket, we can simply remove the aggregate with no other
 * side effects.
 * Otherwise we must propagate the event up.
 */
static void qfq_deactivate_agg(struct qfq_sched *q, struct qfq_aggregate *agg)
{
        struct qfq_group *grp = agg->grp;
        unsigned long mask;
        u64 roundedS;
        int s;

        if (agg == q->in_serv_agg) {
                charge_actual_service(agg);
                q->in_serv_agg = qfq_choose_next_agg(q);
                return;
        }

        agg->F = agg->S;
        qfq_slot_remove(q, grp, agg);

        if (!grp->full_slots) {
                __clear_bit(grp->index, &q->bitmaps[IR]);
                __clear_bit(grp->index, &q->bitmaps[EB]);
                __clear_bit(grp->index, &q->bitmaps[IB]);

                if (test_bit(grp->index, &q->bitmaps[ER]) &&
                    !(q->bitmaps[ER] & ~((1UL << grp->index) - 1))) {
                        mask = q->bitmaps[ER] & ((1UL << grp->index) - 1);
                        if (mask)
                                mask = ~((1UL << __fls(mask)) - 1);
                        else
                                mask = ~0UL;
                        qfq_move_groups(q, mask, EB, ER);
                        qfq_move_groups(q, mask, IB, IR);
                }
                __clear_bit(grp->index, &q->bitmaps[ER]);
        } else if (hlist_empty(&grp->slots[grp->front])) {
                agg = qfq_slot_scan(grp);
                roundedS = qfq_round_down(agg->S, grp->slot_shift);
                if (grp->S != roundedS) {
                        __clear_bit(grp->index, &q->bitmaps[ER]);
                        __clear_bit(grp->index, &q->bitmaps[IR]);
                        __clear_bit(grp->index, &q->bitmaps[EB]);
                        __clear_bit(grp->index, &q->bitmaps[IB]);
                        grp->S = roundedS;
                        grp->F = roundedS + (2ULL << grp->slot_shift);
                        s = qfq_calc_state(q, grp);
                        __set_bit(grp->index, &q->bitmaps[s]);
                }
        }
}

static void qfq_qlen_notify(struct Qdisc *sch, unsigned long arg)
{
        struct qfq_sched *q = qdisc_priv(sch);
        struct qfq_class *cl = (struct qfq_class *)arg;

        qfq_deactivate_class(q, cl);
}

static int qfq_init_qdisc(struct Qdisc *sch, struct nlattr *opt,
                          struct netlink_ext_ack *extack)
{
        struct qfq_sched *q = qdisc_priv(sch);
        struct qfq_group *grp;
        int i, j, err;
        u32 max_cl_shift, maxbudg_shift, max_classes;

        err = tcf_block_get(&q->block, &q->filter_list, sch, extack);
        if (err)
                return err;

        err = qdisc_class_hash_init(&q->clhash);
        if (err < 0)
                return err;

        max_classes = min_t(u64, (u64)qdisc_dev(sch)->tx_queue_len + 1,
                            QFQ_MAX_AGG_CLASSES);
        /* max_cl_shift = floor(log_2(max_classes)) */
        max_cl_shift = __fls(max_classes);
        q->max_agg_classes = 1<<max_cl_shift;

        /* maxbudg_shift = log2(max_len * max_classes_per_agg) */
        maxbudg_shift = QFQ_MTU_SHIFT + max_cl_shift;
        q->min_slot_shift = FRAC_BITS + maxbudg_shift - QFQ_MAX_INDEX;

        for (i = 0; i <= QFQ_MAX_INDEX; i++) {
                grp = &q->groups[i];
                grp->index = i;
                grp->slot_shift = q->min_slot_shift + i;
                for (j = 0; j < QFQ_MAX_SLOTS; j++)
                        INIT_HLIST_HEAD(&grp->slots[j]);
        }

        INIT_HLIST_HEAD(&q->nonfull_aggs);

        return 0;
}

static void qfq_reset_qdisc(struct Qdisc *sch)
{
        struct qfq_sched *q = qdisc_priv(sch);
        struct qfq_class *cl;
        unsigned int i;

        for (i = 0; i < q->clhash.hashsize; i++) {
                hlist_for_each_entry(cl, &q->clhash.hash[i], common.hnode) {
                        if (cl->qdisc->q.qlen > 0)
                                qfq_deactivate_class(q, cl);

                        qdisc_reset(cl->qdisc);
                }
        }
}

static void qfq_destroy_qdisc(struct Qdisc *sch)
{
        struct qfq_sched *q = qdisc_priv(sch);
        struct qfq_class *cl;
        struct hlist_node *next;
        unsigned int i;

        tcf_block_put(q->block);

        for (i = 0; i < q->clhash.hashsize; i++) {
                hlist_for_each_entry_safe(cl, next, &q->clhash.hash[i],
                                          common.hnode) {
                        qfq_destroy_class(sch, cl);
                }
        }
        qdisc_class_hash_destroy(&q->clhash);
}

static const struct Qdisc_class_ops qfq_class_ops = {
        .change         = qfq_change_class,
        .delete         = qfq_delete_class,
        .find           = qfq_search_class,
        .tcf_block      = qfq_tcf_block,
        .bind_tcf       = qfq_bind_tcf,
        .unbind_tcf     = qfq_unbind_tcf,
        .graft          = qfq_graft_class,
        .leaf           = qfq_class_leaf,
        .qlen_notify    = qfq_qlen_notify,
        .dump           = qfq_dump_class,
        .dump_stats     = qfq_dump_class_stats,
        .walk           = qfq_walk,
};

static struct Qdisc_ops qfq_qdisc_ops __read_mostly = {
        .cl_ops         = &qfq_class_ops,
        .id             = "qfq",
        .priv_size      = sizeof(struct qfq_sched),
        .enqueue        = qfq_enqueue,
        .dequeue        = qfq_dequeue,
        .peek           = qdisc_peek_dequeued,
        .init           = qfq_init_qdisc,
        .reset          = qfq_reset_qdisc,
        .destroy        = qfq_destroy_qdisc,
        .owner          = THIS_MODULE,
};

static int __init qfq_init(void)
{
        return register_qdisc(&qfq_qdisc_ops);
}

static void __exit qfq_exit(void)
{
        unregister_qdisc(&qfq_qdisc_ops);
}

module_init(qfq_init);
module_exit(qfq_exit);
MODULE_LICENSE("GPL");
MODULE_DESCRIPTION("Quick Fair Queueing Plus qdisc");